1. Field of the Invention
The present invention relates to a technique for an elevator car to perform an emergency operation at a state of emergency such as power failure, and in particular to a method for controlling a rescue operation of an elevator car which can rescue passengers by performing an emergency operation with an electric power generating of a permanent magnet-type synchronous motor when an emergency such as power failure takes place in an elevator system employing the synchronous motor as a lifting motor.
2. Description of the Background Art
When a permanent magnet-type synchronous motor is employed as a lifting motor in an elevator system, a permanent magnet is used as a magnetic field source, and thus a magnetic component current is not necessary. In addition, in general, the permanent magnet-type synchronous motor is more efficient than an induction motor, and accordingly improves efficiency of the whole elevator system and reduces energy consumption. Therefore, the permanent magnet-type synchronous motor has been used in the elevator system. In the elevator system using the permanent magnet-type synchronous motor as the lifting motor, a conventional apparatus for controlling an operation of an elevator car at a state of emergency, such as power failure, and a method therefor will now be described with reference to FIG. 1.
As illustrated in FIG. 1, the conventional apparatus for controlling the operation of the elevator car (hereinafter referred to as `car`) includes: a converter 102 converting an alternating current from a three-phase alternating current power source 101 to a direct current; a condenser 103 charging and smoothing a direct current outputted from the converter 102; an inverter 104 for inverting a direct current outputted from the condenser 103 to an alternating current by switching of a switching device; a synchronous motor 105 driven by an output from the inverter 104; a contactor 105A closed during the power failure for grounding a three-phase output terminal of the synchronous motor 105 through a ground resistance 105B; a current detector 106 detecting a current supplied from the inverter 104 to the synchronous motor 105; a speed and position detector (such as a rotary encoder outputting a pulse signal corresponding to a rotation speed of the synchronous motor) connected to the synchronous motor 105, and detecting a rotation speed of the synchronous motor 105 and a moving position of the car 110; a traction machine 108 receiving a rotation force from the synchronous motor 105, and driving the car 110 and a balance weight 111 in opposite directions; a brake 109 of the traction machine 108; a power failure detector 112 detecting a state where the three-phase alternating current power source 101 is abnormally inputted or interrupted; a controller 113 outputting a speed command driving the synchronous motor 105 during a normal operation, and outputting a corresponding speed command when the power failure or abnormality detection signal is outputted from the power failure detector 112; an inverter controller 114 receiving an output signal from the current detector 106 and the speed and position detector 107, and outputting a pulse width modulation signal according to a control command of the controller 113; and a gate driving unit 115 receiving the pulse width modulation signal, amplifying it to a predetermined level, and outputting it to the inverter 104. The operation of the conventional apparatus for controlling the operation of the elevator car will now be explained.
In the normal operation, the three-phase alternating current power source 101 is converted into the direct current through the converter 102, and smoothed by the condenser 103. The smoothed direct current is inputted into the inverter 104.
In this state, when the controller 113 transmits the speed command to the inverter controller 114, the inverter controller 114 outputs the pulse width modulation signal having a predetermined pattern which is a gate driving signal to the inverter 104 through the gate driving unit 115. Accordingly, the switching devices in the inverter 104 are switched, and thus a three-phase driving voltage is supplied to the synchronous motor 105.
The synchronous motor 105 rotates at a speed corresponding to the inputted three-phase driving voltage, the rotation force thereof is transmitted to the traction machine 108, and thus the car 110 starts to move to a designated floor.
On the other hand, when the emergency such as the power failure is detected by the power failure detector 112, and when the detection signal is inputted to the controller 113, the driving of the inverter 104 is interrupted. At the same time, the brake 109 of the traction motor 108 is operated, and thus the car 110 stops at a current position. An auxiliary power source which is prepared for the emergency state such as the power failure, namely a battery (not shown) is supplied to the controller 113, the contactor 105A is closed according to the control of the controller 113, and thus an output terminal of the synchronous motor 105 is connected to the ground through the contactor 105A and the ground resistance 105B.
In this state, when the brake 109 is released, the car 110 starts to move towards a heavier side between the car 110 and the balance weight 111, and thus the synchronous motor 105 is rotated. Accordingly, a electric power is generated by the synchronous motor 105, that is the synchronous motor 105 operates as a power generator. A generated current flows through the contactor 105A and the ground resistance 105B, and a braking torque is generated in the synchronous motor 105.
Accordingly, in a state where the driving of the inverter stops, the car 110 moves at such a speed that the braking torque of the synchronous motor 105 and the torque by the weight difference between the car 110 and the balance weight 111 could be balanced. When the car 110 reaches to a door zone of the nearest floor, the brake 109 of the traction motor 108 is driven, and thus the movement of the car 110 stops. At this time, the door is opened, and the passengers are rescued.
However, the conventional apparatus for controlling the operation of the elevator car includes the contactor and the resistor in the circuit of synchronous motor and the inverter, and further includes a control circuit in order to short the output terminal of the synchronous motor to the ground by controlling the contactor during the emergency operation, thereby incurring additional expenses. Moreover, the operational speed of the car is determined merely by the weight difference between the car and the balance weight, and the ground resistance value. Accordingly, there is a disadvantage in that the operational speed is varied according to a load status of the car, namely the number of the passengers and cargo.